[Haskell-beginners] Seq question
tim.v2.0 at gmail.com
Thu Apr 19 23:13:48 CEST 2012
Henk-Jan van Tuly is correct. Oops! Sorry I was mis-informed. By the way,
there is an excellent post about this topic on StackOverflow.com. It
covers, seq, weak-head-normal-form, normal form, and thunks. See here:
Hope that makes up for my earlier comment.
On Thu, Apr 19, 2012 at 2:31 AM, Henk-Jan van Tuyl <hjgtuyl at chello.nl>wrote:
> On Wed, 18 Apr 2012 16:45:05 +0200, Brent Yorgey <byorgey at seas.upenn.edu>
> On Tue, Apr 17, 2012 at 02:41:15PM -0700, Tim Perry wrote:
>>> seq evaluates to Weak Head Normal Form (WHNF). WHNF is the first
>>> contructor. So your use of seq only evaluates the first number and the
>>> cons. I.E., it evaluates to:
>> Actually, it doesn't even force the first number. You just get
>> Thunk : Thunk
> A nice way to demonstrate this, is the following GHCi session:
> Prelude> undefined `seq` print "OK"
> *** Exception: Prelude.undefined
> Prelude> [undefined] `seq` print "OK"
> Henk-Jan van Tuyl
> Haskell programming
> Beginners mailing list
> Beginners at haskell.org
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